Simulation

CadSoft EAGLE – now featuring PCBSim!

EAGLE now supports the newly-developed interface for PCBSim, a simulation tool for signal integrity analysis developed by Felicitas Customized Engineering GmbH.

This new ULP is available to all EAGLE users with the current version of the software and offers the following added benefits:

Signal integrity testing before layout to avoid redesigns

Accurate simulation results

Integration in EAGLE and intuitive operation

Affordability through buy-or-lease option

Direct Support from manufacturer

PCBSim simulates the signal propagation of high-speed digital systems based on transmission lines, IBIS- and s-parameter models. The tool allows users to analyze and if necessary correct a design very early in the design cycle for signal integrity issues. This ensures that the signal integrity remains stable throughout the complete transmission path from sender to receiver IC. PCBSim contains a transmission line calculator, an IBIS viewer and an s-parameter editor. In addition, it integrates a complete SPICE simulator with special extensions for the simulation of IBIS- and s-parameter models.

Transmission lines

PCBSim calculates the properties of transmission lines based on the geometry and the PCB material in use. Most important are: characteristic impedance, frequency dependent losses and frequency dependent delay times.

S Parameter Input

For connectors and sockets, vendors usually supply simulation models as s-parameter files in Touchstone format. These files contain simulated or measured fre-quency domain data for a wide frequency range. PCBSim transfers this data to a format suitable for time-domain simulations. Furthermore, inaccuracies in the input data are corrected (passivity, causality, reciprocity).

IBIS Input

BIS models are readily available from all major semiconductor suppliers. They describe the behavior of integrated circuits without exposing any internal design details. IBIS files are converted to a format suitable for time domain simulations with the integrated SPICE engine.

Simulation results

A full-featured SPICE simulation engine is integrated into PCBSim. Felicitas has added special features to the simulation engine in order to accurately and quickly simulate IBIS models and s-parameter models. The example below shows the input signal for the DRAM controller is ringing back and even crossing the threshold again (see dark blue line). This will most likely cause the design to fail.

The following changes have been made to the design in order to rectify the problem: The transmission line impedance has been reduced from 50 to 35Ohm. The input termination of the DRAM has been configured to 40Ohm and that of the controller to 40 Ohm as well. A slower output configuration was selected with the DRAM controller. Series resistors have been tested but did not improve the situation.

The result is that the ringing is greatly reduced and there is now a comfortable safety margin and thus a reliably working design. Some of the modifications would have been impossible to do on the prototype. Furthermore, finding the cause of the problem would have been very difficult with measurements alone.

————————————————————————–EAGLE 6.4.0 – Now with LTspice IV Interface

LTspice IV is Linear Technology’s high performance SPICE simulator, schematic capture and waveform viewer with enhancements and models for simulating switching regulators. LTspice IV provides all SPICE analysis types within the time and the frequency domain. These functionalities are now available for your schematic created with EAGLE. You can download EAGLE 6.4.0 for Windows with the LTspice IV-EAGLE ULP (User Language Program) from the CadSoft website.

This ULP enables the export of EAGLE data into LTspice IV and vice versa. Complete schematic sheets and single schematic groups can be transferred.